The invention relates to a mixer, particularly for use in the microwave and millimetre wave ranges, comprising four two-pole mixing elements which in essence form a ring and are arranged in the region of a junction between at least two wave guides. The first wave guide comprises a slotted line structure and the second waveguide comprises a line structure formed by at least a central line portion and outer line portions arranged around this central portion. At least the line portions of the first wave guide and the central line portion of the second wave guide are provided as layers on the upper surface of a laminar substrate made of a dielectric material.
U.S. Pat. No. 3,678,395 discloses a mixer in four mixer diodes which are arranged so as to form a ring at the junction of a slot-line and a coplanar line extending axially thereto. High-frequency electromagnetic waves are applied to the diodes via the slot-line and the coplanar line. The electromagnetic oscillations formed as mixing products of these waves at the diodes are derived from the diodes via a shunting network formed by inductive lines and capacitors and a transformer network and are applied to the intermediate-frequency output as an intermediate frequency signal.
The prior art mixer has the disadvantage that, in addition to the slot line and the coplanar line complicated components for deriving the mixed products from the intermediate frequency output are required. These components such as wires, capacitors or transformer networks are connected to the lines during the production of the mixer in separate operation processes, for example by soldering, and are consequently the cause of high production costs. Moreover, such circuit components limit the frequency range for the electromagnetic waves applied to the mixer; more specifically the frequency range for the mixed products is significantly limited towards the high frequencies. In addition, at least some of additional circuit elements are difficult to reproduce in actual production, so that large spreads in the electrical properties may occur between individual mixers. Mixers of the above-described construction are also rather delicate and sensitive to mechanical load.